From U.S. Pat. Nos. 3,261,871 (Fritzsche et al. I) and 4,131,624 (Davis et al.); Fritzsche et al. II, CA 62:10457d; L. Horner et al., Tetrahedron Letters, No. 17, pp. 1157-1162 (1965); and G. M. Kosolapoff et al., Organic Phosphorus Compounds, Vol. 1, Wiley-Interscience (New York), 1972, pp. 45-47, it is known that tertiary phosphine oxides can be reduced to the corresponding phosphines by reaction with trichlorosilane in the presence or absence of an amine catalyst and in the presence or absence of a solvent, such as naphthalene, benzene, toluene, diethylene glycol dimethyl ether, glycol dimethyl ether, or diphenyl oxide.
It would be most desirable to be able to conduct the reaction in the absence of a catalyst and at reaction conditions requiring the least energy expenditure and the lowest possible amount of trichlorosilane. However, as indicated in Fritzsche et al. II, Horner et al., and Kosolapoff et al., it has previously been found necessary to employ at least two mol equivalents of trichlorosilane to reduce a phosphine oxide efficiently in the absence of an amine catalyst. Moreover, Fritzsche et al. II show that the uncatalyzed reduction of triphenylphosphine oxide rerequires reaction of about two mols of trichlorosilane with one mol of the oxide at 200.degree. C. for about two hours to get a phosphine yield of 89.7%.